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2goal is to provide data on plume characteristics that may be used to verifymathematical models for thermal plumes.The paucity of prototype data for surface thermal discharges has oftenboen documented. [1], [2] This lack of data on thermal-plume behaviorfostered the development of numerous mathematical models, each attemptingto predict thermal-plume dispersion from shoreline canal discharges. Todate, however, none of those models has been sufficiently verified withprototype data to allow them to be used comfortably in a predictive sense.With a more complete library of plume data at hand, plume models can befurther verified. More importantly, our increased understanding of plumephysics will allow improved models to be developed. Model assumptions maybe checked and improved by analysis of the experimental data. Also, thedata will indicate which of the observed characteristics of thermal plumesmay be predicted by present-day deterministic models. The significance ofthe data and analysis given below transcends shoreline surface discharges:plumes from submerged discharges eventually reach the surface and disperseby the same mechanisms as surface plumes under like environmental conditions.To date, the majority of analytical models for surface thermal plumeshave been verified using only hydraulic scale model data or sparse fielddata. Most of the available data on surface thermal plumes has been ac-quired in hydraulic-model studies. Nearly all of this data are from un-distorted models of the near-field region of the plume. Such physicalmodels are flexible and allow numerous tests to be made, each test varyingimportant plume parameters. In this way, various physical phenomena in-volving plume dispersion may be studied under laboratory-controlled con-ditions. This provides a definite advantage in any basic study of thermalplume dispersion. These undistorted hydraulic models, however, cannotadequately simulate far-field phenomena such as surface-heat loss, inter-facial friction, ambient turbulence, and wind and wave effects. Thesephenomena become important in regions of the plume where jet momentum hasessentially dissipated. The impossibility of simultaneously satisfying allthe appropriate model-scaling parameters in either an undistorted or dis-torted model leads to only a partial picture of the plume.Most of the prototype field data available in the literature aresketchy in that the data are not sufficiently refined to extract the majorplume characteristics. breover, in much of the data, not all the import-ant plume parameters were measured. Only recently have some large effortsbeen undertaken other than by Argonne National Laboratory, attempting toprovide more complete sets of data. Noteworthy is the data collected at theLakeview Generating Station on Lake Ontario, [3] the Pilgrim Plant in Mass-achusetts on Cape Cod Bay, [4] and the Surry Plant on the James River. [5]As long as the value of a mathematical model remains determined by how wellit predicts results in the field, thorough monitoring programs will be re-quired to obtain a large body of data under a wide range of conditions tofully and fairly evaluate and improve these models.2. THE PLANT SITES AND DATA ACQUISITIONThree-dimensional temperature data were taken [6], [7], [8] at foursites of heated surface discharges on Lake Michigan during the 1971, 1972,and 1973 field years. Chosen were the Point Beach, Waukegan, and State Linesites on the western or-5outhwestern shore of the Lake, and the Palisadessite on the eastern shore. Figure 1 sketches the outfall and shoreline con-figuration of these plants. Table I (appearing with Fig. 4) summarizes thebasic characteristics of the outfalls and their warm-water discharges. ThePoint Beach Plant has two identical units with condenser cooling water dis-